1. Field of the Invention
The present invention relates to a method of compensating sheet feeding errors in an ink-jet printer, and more particularly, to a method of compensating a feeding error of a sheet fed in an X direction, using an optical sensor that travels in a Y direction in an ink-jet printer. The present invention also relates to a method of compensating a feeding error in every section of a circumference of a feeding roller by equally dividing the circumference of the feeding roller by n sections.
2. Description of the Related Art
In general, an ink-jet printer includes a carriage on which an ink cartridge is mounted to print an image on a sheet of material and which makes a printhead that ejects ink move back and forth in a primary scanning direction (a Y direction), and a feeding roller, which moves the sheet in a secondary scanning direction (an X direction). A printer using the feeding roller requires precise control of the feeding roller. If control of the feeding roller is unstable during a printing operation, a black line may occur due to printing superimposition, or a white space may occur due to a widened space between lines.
FIG. 1 schematically illustrates the structure of an apparatus in which a conventional method of compensating sheet feeding errors in an ink-jet printer is used. Referring to FIG. 1, a carriage 10 in an ink-jet printer (not shown) travels in a Y direction perpendicular to a sheet feeding direction (an X direction) above a platen (not shown) on which a sheet P of material is placed. At least one ink-jet cartridge 20 is mounted on the cartridge 10, and a printhead (not shown) in which a plurality of nozzles (not shown) are formed is placed at a bottom of the ink cartridge 20. One side of the cartridge 10 is fixedly mounted on a traveling belt 30, and the other side thereof is mounted to slide on a guide rail 31. Thus, the cartridge 10 is driven by an electromotor 33 via a traveling belt 30, in a back and forth motion in the Y direction. A control unit 40 precisely controls the Y reciprocating movement of the cartridge 10 by counting the number of pulse signals generated in a linear encoder 12 attached to the carriage 10, when the linear encoder 12 passes over a plurality of marks 14 of an encoder strip 16 formed at regular intervals.
Meanwhile, the sheet P is transferred by a feeding roller 50 in a secondary scanning direction (the X direction). The feeding roller 50 is moved via a feeding roller driving motor 51, moving a predetermined angle each time it moves. An encoder disc wheel 52 is mounted on a circumference of one end of the feeding roller 50. A rotary encoder sensor 53 to measure a rotation angle of the encoder disc wheel 52 generates pulse signals corresponding to equally spaced slits (52a) formed on a circumference of the encoder disc wheel 52, and the control unit 40 controls a rotation angle of the feeding roller 50, i.e., a transfer distance in the X direction of the sheet P, by counting the number of the pulse signals.
Meanwhile, to verify the precision of the rotary encoder sensor 53, a linear encoder sensor 60 is fixedly placed in a moving direction of the sheet P, and the length of the sheet P, which is actually fed, is measured. That is, the moving distance of the sheet P read by the linear encoder sensor 60 is measured using a linear scale encoder strip 61 that moves together with the sheet P. By comparing the actual moving distance of the sheet P with a moving distance on the circumference of the feeding roller 50 read by the rotary encoder sensor 53, an error of the rotary encoder sensor 53, i.e., a feeding error caused by the curvature and abrasion of the surface of the feeding roller 50, is measured, and the feeding roller driving motor 51 is controlled to compensate for the measured error.
However, the conventional method of compensating sheet feeding errors in an ink-jet printer is performed to compensate an error of the rotary encoder sensor 53 caused by the feeding roller 50. To perform the method in an ink-jet printer, a linear encoder sensor to detect an error should be attached to the printer in an X direction, the output of the linear encoder sensor should be connected to an additional measuring system, and a linear scale encoder strip should be attached onto a sheet of material. Thus, a user cannot perform the method easily.
In addition, to calibrate a printer having a high resolution, the method requires a linear encoder sensor having a high resolution to detect a linear strip.